As one type of capacitor, there is a film capacitor having a structure in which a resin film having flexibility is used as a dielectric body and first and second counter electrodes opposed to each other are arranged with the resin film sandwiched therebetween. A film capacitor usually has an approximately cylindrical shape formed by winding a resin film as the dielectric body described above, and first and second external terminal electrodes are formed on a first end face and a second end face of the cylinder opposed to each other, respectively. The first counter electrode is electrically connected to the first external terminal electrode and the second counter electrode is electrically connected to the second external terminal electrode.
As a dielectric resin film for the above-mentioned film capacitor, it is described, for example, in WO 2010/101170 A (Patent Document 1) to use a dielectric resin film made of a thermosetting resin. The dielectric resin film made of a thermosetting resin has a feature of high heat resistance and excellent voltage endurance.
As a resin having particularly excellent voltage endurance, a resin formed by curing a mixed liquid of polyvinyl acetoacetal (PVAA) and tolylene diisocyanate (TDI), disclosed in Patent Document 1, has a high withstand voltage of 350 V/μm at 125° C.
On the other hand, in recent years, frequencies of electronic devices increase and better high frequency characteristics of electronic components are increasingly required. A major problem in a capacitor is a dielectric loss tangent (tan δ) at high frequency. The dielectric loss tangent is preferably lower, and is ideally zero. A high value thereof causes energy loss and heat generation associated therewith, resulting in the problems that the operation of a high frequency circuit becomes unstable or the life of an electronic component is shortened. The PVAA/TDI described above has a problem that the dielectric loss tangent exceeds 0.75% at 125° C. and at a frequency of 1 kHz based on the data disclosed in Patent Document 1, and therefore use of the PVAA/TDI is difficult in applications where heat generation causes a problem.    Patent Document 1: WO 2010/101170 A